1. Field of the Invention
This invention relates generally to fuel delivery systems for an internal combustion engine and, more particularly, toward a fuel delivery module immersed in a tank containing liquid fuel having a fuel level sender unit affixed thereto.
2. Related Art
Typical automotive fuel systems include in-tank mounted fuel delivery modules which contain a cup-like reservoir for containing a limited quantity of fuel within the tank. A fuel pump inside the reservoir withdraws the fuel from the reservoir and delivers it to an internal combustion engine. Fuel in the reservoir is continually replenished by the surrounding quantity of fuel in the fuel tank. However, as the level of fuel in the tank falls, the limited quantity of fuel in the reservoir provides a buffer of fuel around the fuel pump. When the vehicle makes hard turns or navigates steep inclines during low fuel conditions, the reservoir helps assure an adequate quantity of fuel is available to the pump.
Typically, a fuel delivery module will also contain a vapor vent valve and/or recirculation system, together with a fuel level sensing float and accompanying electronics. The reservoir functions, therefore, as a container around the fuel pump for collecting the reserve supply of fuel for the pump to use during conditions when it might otherwise be temporarily lacking fuel, as well as a support housing for the level sensing electronics and hardware.
The fuel delivery module has the capability of detecting and measuring the level of fuel in the fuel tank by way of its fuel level sender unit. The fuel level sender unit is typically attached to the reservoir and includes a float mechanism. The float mechanism is pivotally mounted to the fuel level sender assembly, which interacts with circuitry to develop a measure of the level of fuel in the tank based on the buoyant position of the float.
The method by which the fuel level sender unit is attached to the reservoir has been a source of much attention over the years. For reservoir housings made of injection molded plastic, it has been common to mold in place fittings of the self-locking variety to “snap-fit” the fuel level sender carrier in position. The carrier comprises a card-like mounting structure upon which the float mechanism is pivotally supported. The problem with the snap-fit technique, however, is that it is generally limited to applications which use plastic injection molded reservoirs. Injection molding is a fairly expensive form of manufacturing due to the high cost of tooling and its relatively slow through-put rates. A further disadvantage is the single, fixed orientation of the fuel level sender carrier relative to the reservoir. That is, the carrier cannot be moved or relocated relative to the reservoir once snapped in position. This, in turn, could affect the measurement qualities of the fuel delivery module depending upon the specific fuel tank in which it is installed and any running model changes which might be introduced to the fuel tank or to the module mounting arrangement.
Some fuel delivery module applications call for the reservoir to be made from aluminum or other metal-based material. In order to attach the fuel level sender unit to a non-plastic housing, such as aluminum, for example, the possible choices are limited in view of certain practical considerations like fabrication cost and the properties of the reservoir material. Some prior art applications have taught a method of resistance welding a metallic frame to an aluminum reservoir. The frame would thus comprise the carrier for the fuel level sender. While this technique allows some degree of variability in positioning the carrier on the module reservoir, it has proven problematic in practice because welding to aluminum is highly process sensitive due to aluminum's conductivity and oxidation potential. In addition, the inherent process variation characteristic of welding can be a concern.
Accordingly, there is a need for an improved method of attaching a fuel level sender unit to the reservoir of a fuel delivery module which allows variable positioning of the sender unit relative to the module reservoir and which can be accomplished on any type of housing composition, be it aluminum, plastic, or other material.